Summary: 21
Where Are the Switches on This Thing?
L. F. Abbott
Introduction
Controlled responses differ from reflexes because they can be turned off and
on. This is a critical part of what distinguishes animals from automatons. How
does the nervous system gate the flow of information so that a sensory
stimulus that elicits a strong response on some occasions, evokes no response
on others? A related question concerns how the flow of sensory information is
altered when we pay close attention to something as opposed to when we
ignore it. Most research in neuroscience focuses on circuits that directly re-
spond to stimuli or generate motor output. But what of the circuits and
mechanisms that control these direct responses, that modulate them and turn
them off and on?
Self-regulated switching is vital to the operation of complex machines such
as computers. The essential building block of a computer is a voltage-gated
switch, the transistor, that is turned off and on by the same sorts of currents
that it controls. By analogy, the question of my title refers to neural pathways
that not only carry the action potentials that arise from neural activity, but
are switched off and on by neural activity as well. By what biophysical mech-